Thailand's Andaman Sea: North and South – April 21–28, 2025
Exploring Thailand’s Underwater National Treasures
As the sun rose over Ranong, we welcomed an enthusiastic group of divers from the USA, France, Brasil, and Switzerland aboard the MV Smiling Seahorse. Our journey would take us through some of Thailand’s most iconic national parks—from Surin and Similan to Lanta and Tarutao—each with its own unique seascape and underwater wonders. Spirits were high as we set a course for the famed Surin Islands to begin our underwater adventure. All pictures on this blogpost were taken by our distinguished guests.
As the sun rose over Ranong, we welcomed an enthusiastic group of divers from the USA, France, Brasil, and Switzerland aboard the MV Smiling Seahorse. Our journey would take us through some of Thailand’s most iconic national parks—from Surin and Similan to Lanta and Tarutao—each with its own unique seascape and underwater wonders. Spirits were high as we set a course for the famed Surin Islands to begin our underwater adventure. All pictures on this blogpost were taken by our distinguished guests.
Day 1: Surin National Park – A Colorful Beginnin
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We started gently at Koh Chi with a smooth check dive. A green turtle greeted us calmly near the surface, while beneath us a flurry of life unfolded. Schools of fusiliers flashed by in silver and gold, flanked by lionfish lurking near coral outcrops. A flabellina nudibranch caught our eye, soon followed by a brilliant Thecacera, better known as the pikachu nudibranch. Moray eels slithered through the cracks, and a stonefish lay well camouflaged in the sand.
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Seahorse - Photo by Garry Perrenoud
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​At Richelieu Rock, the action exploded in all directions. Rainbow runners swept past in schools, chased by jackfish and trevallies. A longface emperor patrolled the reef edge while a ghost pipefish hovered in the current. We marveled at a delicate tiger tail seahorse wrapped around a whip coral and delighted in sightings of harlequin shrimp, white-eyed and giant morays, and a baby mimic octopus dancing across the sand.
Anemone crabs, mackerel, tuna, and hairy shrimp all made appearances, with dogtooth tuna cruising in the distance and clouds of barracudas circling overhead. Our night dive on Richelieu Rock revealed the reef's secret nocturnal side. Among the crustaceans were banded coral shrimps, squat lobsters, transparent cleaner shrimps, and an energetic boxer shrimp. Decorator spider crabs crept slowly across the corals, while a bold red crab was caught pulling a soft coral free—redecorating the reef, it seemed, in its own way. A trumpetfish patrolled the shallows as scorpionfish hunted under the beams of our torches. |
​Day 2: Similan National Park – Granite Giants and Pelagic Glory
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At Koh Tachai Pinnacle, the visibility stretched on forever, revealing a stunning cast of marine life. Giant groupers peered out from overhangs, and bluefin trevallies streaked past in hot pursuit of silvery baitballs. Blacktip sharks cruised the periphery, while massive schools of yellowback and blueback fusiliers lit up the water. We also admired pickhandle barracudas, giant snappers, and dogtooth tuna patrolling in the blue, and couldn’t miss the clown triggerfish darting between boulders. Lobsters peeked from crevices and surgeonfish grazed along the reef walls.
At Koh Bon, we were lucky enough to spot a whitetip reef shark gliding gracefully across the reef, followed by a school of batfish shadowing us from a respectful distance. Giant trevallies patrolled the deeper sections while groups of parrotfish crunched away at the reef. In the coral gardens, butterflyfish, wrasses, and Moorish idols added dazzling detail to the scene. ​ Our blackwater dive that night was a dreamlike journey into the abyss. We were met by strange and mesmerizing creatures: larval flounders fluttering in the current, translucent baby squids, flying gurnards spreading their wing-like fins, and a baby sea elephant drifting gently by. Even a juvenile mantis shrimp made a curious appearance. |
Tiger egg cowrie - Photo by Gary Perrenoud
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Anemonefish - Photo by Gary Perrenoud
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​Day 3: Similan National Park – Rays, Reefs, and Swim-Throughs
Three Trees delivered calm water and stunning white sand patches covered in garden eels. A porcupine stingray and blue-spotted ray swept by, while above us schools of fusiliers and snappers moved in synchronized waves. Curious trumpetfish hovered and gobies danced along the sandy slopes.
Elephant Head Rock was majestic as always. We drifted through its cavernous swim-throughs, surrounded by walls adorned with giant sea fans and hunting giant moray eels. A white-tip shark slipped by, and above us an eagle ray soared across the sunbeams. We caught sight of a mature yellow boxfish before it tucked into a crevice, while blue-lined groupers and bannerfish hovered near the edges of the boulders.
Elephant Head Rock was majestic as always. We drifted through its cavernous swim-throughs, surrounded by walls adorned with giant sea fans and hunting giant moray eels. A white-tip shark slipped by, and above us an eagle ray soared across the sunbeams. We caught sight of a mature yellow boxfish before it tucked into a crevice, while blue-lined groupers and bannerfish hovered near the edges of the boulders.
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At West of Eden, a vibrant coral garden greeted us, bursting with color and activity. Fusiliers, parrotfish, groupers, and an array of surgeonfish filled the reef. A hawksbill turtle paddled calmly overhead, and a bold eagle ray buzzed us in the blue. Chromodoris nudibranchs and flabellinas dotted the walls, while a large tuna charged past at the end of the dive.
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Garden eel- Photo by Garry Perrenoud
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​Day 4: Koh Lanta National Park – Deep Blue Action
Mantis Shrimp with eggs - Photo by Aiara Ponce de Leon
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We spent the entire day diving the twin giants of the South: Hin Daeng and Hin Muang. The reef was electric—ghost pipefish floated in the current, while juvenile clown triggerfish and sweetlips played along the reef. Schools of rainbow runners swept by like silver bullets.
​ ​We spotted several Wahoos, giant trevallies and bluefin trevallies on the hunt, and even found a massive clown frogfish and hairy shrimps expertly camouflaged on the wall as well as a mantis shrimp carrying its eggs! |
Giant Clown Frogfish - Photo by Aiara Ponce de Leon
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Algae / Hairy Shrimp (Phycocaris simulans) - Photo by Aiara Ponce de Leon
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The sunset dive was full of movement and macro life. Helmet crabs and decorator crabs scuttled across the reef while zebra moray eels and common morays hunted along the slopes. Nudibranchs—chromodoris fidelis, annulata, risbecia, and geminus—dotted the rocks like confetti, with bornella anguilla curling through the soft corals.
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​Day 5: Koh Tarutao National Park – Reef Riches and Tropical Surprises
​At 8 Mile, action unfolded fast. Jackfish surged through schools of damsels, while great barracudas enjoyed a spa treatment at a midwater cleaning station. Stonefish crouched on coral heads, hiding in plain sight, while sweetlips and snappers pulsed in the current. Surgeonfish and groupers mingled along the reef, flanked by bannerfish and goatfish.
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At Steps, we enjoyed sightings of coral catsharks, triggerfish, angelfish, and a group of blackspot wrasses working over the coral. At Stonehenge, a devil scorpionfish waited in ambush, while a pair of cuttlefish hovered over the sand. We saw blue dragons clinging to overhangs, as well as a mix of tomato, saddleback, and false clown anemonefish. |
Coral Catshark at Steps (Atelomycterus marmoratus) - Photo by Aiara Ponce de Leon
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At Koh Taru, baby yellow fusiliers filled the reef, flashing like lightning. A baby yellow boxfish stole hearts with its wobbling swim, while a large star puffer looked on with sleepy eyes. Indian Ocean walkman scorpionfish and banded pipefish made rare appearances to round off the day.
Day 6: A Final Sweep Through the South Andaman
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Back at Hin Daeng, batfish and fusiliers welcomed us again, with chromodoris nudibranchs adding pops of color. Hin Muang gave us a fantastic encounter with a clown frogfish, alongside a powerful school of wahoo and a mix of giant and bigeye trevallies.
​ At Koh Haa’s Cathedral, the ethereal beams of sunlight filtering through the swim-through lit up clouds of glassfish, flabellinas, and chromodoris albopunctata. In the Chimney, we added wrasses, gobies, damselfish, and a handful of skunk anemonefish to our growing species list. |
Coral closeup by Garry Perrenud
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Pretty Nudis by Aiara Ponce de Leon
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Day 7: A Grand Finale
At Shark Point, our last dive brought us past massive barrel sponges teeming with life. Schools of fusiliers, chromodoris annulata, and a sly scorpionfish shared the reef with sand-colored flounders and the ever-graceful bannerfish. A pair of butterflyfish saw us off as we began our slow ascent.
​As we returned to Phuket, the boat was buzzing with stories, laughter, and glowing memories. From turtles and seahorses to blackwater aliens and reef giants, this trip through Thailand’s best dive sites had truly lived up to its name. |
Koh Bida Nok delivered a dramatic last day. A blacktip reef shark cruised by as a yellowtail seahorse clung to coral nearby. A banded sea snake slipped between rocks while cuttlefish hovered in the blue.
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Video of the trip by our lovely friend Aiara
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